1. Field of the Invention
The present invention relates to a driving method for an ultrasonic motor and an apparatus using the same.
This application is based on Japanese Patent Application No. 2005-182991, the content of which is incorporated herein by reference.
2. Description of Related Art
Recently, ultrasonic motors have been drawing attention as a new type of motor replacing electromagnetic motors. Ultrasonic motors have the following advantages over known electromagnetic motors:
1) Ultrasonic motors are capable of high torque without using gears;
2) Ultrasonic motors have holding force when powered off;
3) Ultrasonic motors have high resolution; and
4) Ultrasonic motors are quiet.
A known method of driving such ultrasonic motors is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 07-131986. More specifically, in the technique disclosed in Japanese Unexamined Patent Application Publication No. 07-131986, when an ultrasonic motor is to be rotationally driven, two-phase alternating signals are applied to excite traveling elastic waves so that the ultrasonic motor is driven stably and efficiently without causing abnormal noise or vibration during the startup operation of the ultrasonic motor.
Unfortunately, the above-described known technique is problematic in that when alternating signals are applied, traveling elastic waves are abruptly excited, which causes sticking and slipping and leads to unstable driving of the ultrasonic motor at the initial driving time. The known technique has another disadvantage in that large drive noise is generated during the initial driving time of the ultrasonic motor.